ABSTRACT The overall objective of this proposed research is to develop improved methods for the detection and diagnosis of dental caries (dental decay). New, more sophisticated diagnostic tools are needed for the detection and characterization of caries lesions in the early stages of development. If carious lesions are detected early enough, before cavitation, then they can be arrested/remineralized by non-surgical means. Clinicians need new imaging technologies employing non-ionizing radiation to aid in caries diagnosis and management, to reliably track the course of lesions over an extended time period in order to determine whether the lesion is active and expanding or whether it has been arrested, and determine if intervention is needed. Short wavelength infrared light (SWIR) is defined as light from 1000-2500-nm beyond the reach of conventional silicon based sensors. Longer wavelengths offer significant advantages for imaging caries lesions including higher contrast between sound and demineralized tissues due to reduced light scattering and higher water absorption and reduced interference from stains that do not absorb light at wavelengths greater than 1200-nm. We hypothesize that the wavelength region from 1300 to 2300-nm offers the greatest potential for new optical imaging modalities. The overall objectives of this proposal will be achieved through the following specific aims. (1) To test the hypothesis that imaging with light in the previously unexplored wavelength range from 1700-2350-nm in the SWIR will yield increased contrast between sound tissues and demineralized tissues on tooth coronal and root surfaces. (2) To test the hypothesis that multispectral and multimodal SWIR imaging approaches can be used to significantly improve the diagnosis of caries lesions. (3) To test the hypothesis that imaging at longer wavelengths in the SWIR can be used to improve the diagnosis of lesions on tooth proximal surfaces by assessing cavitation and deeply penetrating lesions. It is likely that if these studies and future clinical trials are a success, that this novel technology for imaging dental hard tissue will be employed for the detection, diagnosis and monitoring of early carious lesions without the use of ionizing radiation, thereby enabling conservative non-surgical intervention and the preservation of healthy tissue structure.